Deep Dive: T8A05
The correct answer is C: CW. CW (Continuous Wave, Morse code) has the narrowest bandwidth of the listed signal types. CW signals are essentially unmodulated carriers that are keyed on and off, requiring only the bandwidth needed for the keying speed (typically 100-200 Hz for normal speeds). For amateur radio operators, CW's narrow bandwidth makes it excellent for weak-signal work, DX operation, and situations where bandwidth is limited. It's the most spectrum-efficient mode, allowing many stations to operate in a small frequency range.
Why Other Answers Are Wrong
Option A (FM voice): Incorrect. FM voice requires about 15 kHz bandwidth, much wider than CW. FM's wide bandwidth provides good audio quality but uses more spectrum. Option B (SSB voice): Incorrect. SSB voice requires about 3 kHz bandwidth, wider than CW. SSB is efficient but not as narrow as CW. Option D (Slow-scan TV): Incorrect. Slow-scan TV requires several kHz of bandwidth, much wider than CW. Video signals need significant bandwidth.
Exam Tip
CW = narrowest bandwidth. Think 'C'W = 'C'ontinuous 'W'ave = 'C'ompact 'W'idth. CW uses only 100-200 Hz, making it the narrowest. FM (~15 kHz) and SSB (~3 kHz) are much wider.
Memory Aid
CW = narrowest bandwidth. Think 'C'W = 'C'ontinuous 'W'ave = 'C'ompact 'W'idth (~150 Hz). Narrowest of all modes. FM (~15 kHz) and SSB (~3 kHz) are much wider.
Real-World Example
On a crowded band, CW operators can fit many stations in a small frequency range because each CW signal uses only about 150 Hz. In the same space, you might fit only one FM signal (15 kHz) or a few SSB signals (3 kHz each). CW's narrow bandwidth makes it ideal for weak-signal work and efficient spectrum use.
Source & Coverage
Question Pool: 2022-2026 Question Pool
Subelement: T8A
Reference: 2022-2026 Question Pool · T8 - Signals and emissions
Key Concepts
Verified Content
Question from the official FCC Technician Class pool. Explanation reviewed by licensed amateur radio operators and mapped to the T8A topic.